Many of the high solids automotive coatings presently in use are based upon polymeric systems comprised of a binder comprising either polyester-based or polyacrylic-based polyols and crosslinking agents therefor. These coatings are generally supplied as “one-pack” or “two-pack” systems.
In a typical one-pack system, all of the coating ingredients are combined into one storage-stable mixture. Upon application, the polyol component is crosslinked, generally with an aminoplast resin (such as a melamine resin) or a blocked isocyanate, usually under heat cure conditions of 120° C. or above. In a typical two-pack system, the polyol component is combined with a crosslinking agent, generally an isocyanate, shortly before application, with curing being conducted at ambient and/or elevated temperatures.
Coatings used for painting motor vehicles and repairing the original paint are desired to have good physical properties such as hardness, mechanical strength, and resistance to water, acids, and solvents. The coatings are also desired to have good appearance properties, providing smooth films and a high gloss and high distinctness of image. It is also desirable that such coatings have an excellent car wash, scratch, and mar resistance.
A large number of cars and transport vehicles are coated with a multilayer topcoat system wherein an unpigmented clearcoat is applied over a pigmented basecoat. Both solvent borne and water borne clearcoats and basecoats are in use. So-called metallic basecoats comprise metallic flakes.
For environmental reasons, it is becoming increasingly important to develop polymeric systems with low solution viscosities, which permit the formulation of high solids coatings with low application viscosities suitable for spraying. High solids coatings (generally 50 wt. % or greater solids) significantly decrease the amount of volatile organic compounds (VOC) entering the atmosphere upon drying/curing of the coating.
One way to achieve a lower solvent content is to use so-called high-solids compositions. Such compositions comprise a relatively high level of non-volatile materials such as film forming polymer, pigments, and fillers, and a relatively low level of organic solvent. A problem when formulating high-solids coating compositions is that such compositions have an unacceptably high viscosity due to the high molecular weight of the conventional film forming polymer. The high viscosity gives rise to problems in spray application with poor paint atomization and poor flow-out and, consequently, low gloss levels and poor appearance.
The use of low-molecular weight film forming polymers results in adequate application viscosities. However, coating composition based on this type of resins generally use the crosslinker to have acceptable film properties. But scratch and mar resistance may be negatively influenced, especially in 2K coating compositions.
Polyurethane polyols, such as those described in U.S. Pat. No. 6,753,386, are presently utilized in coating formulations to improve scratch resistant coatings.
However, these polyurethane polyols may be expensive to produce based on the high cost of polyisocyanates. Further, although these polyurethane polyols are effective at low temperatures, it is desirable to have a polyol which has more reactivity in low bake systems.
Melamine formaldehyde resins are utilized as crosslinkers in many coating applications. However, due to their reactivity, these resins have a predisposition toward self-condensation making them difficult to utilize. Further, melamine formaldehyde crosslinkers are generally utilized for high bake systems.
In EP-A-0 199 605, pigment pastes, mainly for use in paints and ink, comprising a pigment dispersing agent and, optionally, an organic solvent are disclosed. The pigment dispersing agent may be obtained by co-condensing a triazine-type amino compound, formaldehyde, a diol, and a monohydric alcohol.
WO 2003/091347 relates to polymeric dispersion additives with hyperbranched structures and the use of modified and unmodified hyperbranched polyurethanes.
WO 2003/029318 relates to polyurethane block copolymers containing one or more hydrophilic groups and the use of such copolymers as crosslinkable dispersion additives for colorant preparations.
U.S. Pat. No. 4,271,286 relates to a process for the preparation of methylolaminotriazines etherified with alkanols having per mole of the aminotriazine 0.6n to 2n methyol groups to the extent of 30% to 60%, n being the number of amino groups in the amino triazine.
GB patent no. 1465426 relates to low viscosity mixture of etherified emthyolaminotriazines with average degree of emthylolation substantially 50% to 80% for use with hydroxyl containing resins.
U.S. Pat. No. 3,293,212 relates to reaction products of hexaalkyl ethers of hexamethylolmelamines and bisphenols.
DE patent no. 1620217 relates to a cleaning process for removing residual glycol in melamine mixture.
U.S. Pat. No. 4,528,344 discloses an ungelled, crosslinkable, hydroxylgroup-containing resin having a molecular weight of less than 4500, which is the reaction product of a nonaromatic polyol having a molecular weight of less than 230, and an aminoplast.
It is an object of the present invention to provide low viscosity oligomeric polyols for use in coating compositions.
It is a further object of this invention to provide low viscosity oligomeric polyols for use in coating compositions that will cure under ambient and forced dry conditions while providing good application and performance characteristics.
It is also an object of this invention to provide low viscosity oligomeric polyols for use in coating compositions with a low VOC.
It is additionally an object of this invention to provide low viscosity oligomeric polyols for use in coating compositions resulting in dried and cured coatings with an improved scratch resistance in particular compared to coatings prepared from a coating composition comprising an acrylic polyol and a polyisocyanate compound.